Many different types of welding machines have been used in the prior art. One such prior art welding machine includes a full wave, three-phase, phase controlled welding power supply. For example, the Miller Dimension.TM. series of welding machines use a three-phase input and provide a constant current (CC) or a constant voltage (CV) output.
Another prior art welding machine is the Miller Big Blue.TM. 400D welding machine, which is an engine driven welding generator, and can also be operated in a CC output or CV output (with an added module). The output of this welding generator can be used directly to stick weld, or to provide power to a wire feeder for MIG welding.
Some engine driven welding machines include two power supplies driven by a single engine/generator. One example of this is the MQ Power Dualweld 400.TM.. Generally, such dual output welding machines include the ability to select between an independent and combined mode. In the independent mode output power from the power supplies is provided independently to two pairs of output studs, and the machine effectively acts as two independent welding power supplies (both connected to a single generator). The controller includes two current magnitude selectors, one associated with a first output, and the other associated with the second output.
In the combined mode the outputs of both power supplies are combined, or placed in parallel, to form a single welding output. Thus, in this mode, the maximum output is twice that of the output in the independent mode of operation.
There are several drawbacks with the prior art dual output machines. First, when operating in the combined (parallel) mode, two output controls are used in the prior art to control a single output. This is because the output control for each power supply continues to control its respective power supply, even though the outputs are being combined to a single welding output. Thus, to balance the output between the two power supplies (which reduces the likelihood of overheating), one must adjust both output selectors to be in the same position.
Another disadvantage of dual output machines is that when operating in the combined (parallel) mode a CV output cannot be provided because the power supplies are parallel, and might not share the current. The prior art overcomes this problem by not providing a CV output in dual output, phase controlled, machines (even when the machine is operating in the independent mode).
Another prior art dual welding machine includes a generator used to power one or more inverters. The inverters are operated independent of one another, and cannot have their outputs combined to provide a relatively greater magnitude output in CV mode.
Accordingly, a dual output welding machine that provides for a single control of the output when operating in the combined mode is desirable. Additionally, such a welding machine will preferably be capable of providing a CV output when operating in the independent mode.
Many engine driven/generator welding power supplies have a drooping VA curve, wherein as the current increases, the output from the weld windings decreases. Accordingly, an engine driven/generator welding power supply that compensates for a drooping VA curve, by increasing the voltage when the current increases, is desirable.